US4684253A - Apparatus for carrying out spectral analysis - Google Patents

Apparatus for carrying out spectral analysis Download PDF

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Publication number
US4684253A
US4684253A US06/570,930 US57093084A US4684253A US 4684253 A US4684253 A US 4684253A US 57093084 A US57093084 A US 57093084A US 4684253 A US4684253 A US 4684253A
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Prior art keywords
grating
gratings
diffraction
spectral
wavelength
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US06/570,930
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English (en)
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Karl P. C. Lindblom
Sonja A. Engman
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SCANOPTICS VALLIKATU 17 SF-02600 ESPOO 60 Oy
SCANOPTICS Oy
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SCANOPTICS Oy
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Assigned to SCANOPTICS OY, VALLIKATU 17, SF-02600 ESPOO 60, reassignment SCANOPTICS OY, VALLIKATU 17, SF-02600 ESPOO 60, ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: ENGMAN, SONJA A. C., LINDBLOM, KARL P. C.
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/12—Generating the spectrum; Monochromators
    • G01J3/18—Generating the spectrum; Monochromators using diffraction elements, e.g. grating

Definitions

  • the present invention relates to an apparatus for carrying out spectral analysis comprising means for leading the radiation into the apparatus, means for recording the produced spectrum and diffraction grating means for dispersing the incident radiation.
  • diffraction gratings As wavelength dispersing optical means for dividing optical radiation into wavelength components.
  • spectral apparatuses which, in addition to the grating, usually have an entrance slit through which the optical radiation to be analyzed is admitted to the apparatus, whereafter the diffraction grating together with other optical means produces an image of the entrance slit on a focal plane so that optical radiation of different wavelengths is reproduced in different locations on said plane.
  • the recording of the spectrum i.e. the measurement of the intensity of the different wavelength components is usually carried out photoelectrically.
  • Spectral instruments provided with photoelectric recording are usually called spectrometers.
  • a slit In certain types of spectrometers a slit, a so-called secondary slit, is used also in the focal plane behind which a photoelectric detector is positioned. The recording of the spectrum then takes place so that by rotating, for example, the grating the different wavelength components are made to pass the slit sequentially and are recorded by the detector.
  • a spectrometer of this kind is called monochormator.
  • Spectrometers provided with several secondary slits and detectors are analogically called polychromators.
  • ⁇ denotes the so-called angle of incidence, i.e. the angle which the optical radiation incident on the grating forms with the normal to the grating surface, hereinafter called grating normal.
  • the quantity ⁇ analogically denotes the angle which the outgoing optical radiation forms with the grating normal after diffraction in the grating surface.
  • the quantity ⁇ denotes the wavelength of the optical radiation, the quantity d the distance between the grooves in the grating surface, and m the so-called spectral order. This is an integer implying that the same wavelength can be dispersed through diffraction in different well-defined diffraction angles corresponding to different values of the integer m. In the same spectral order different wavelength components give rise to diffraction at different diffraction angles ⁇ .
  • n indicates the refractive index of the gas which surrounds the grating surface. This has approximately the value 1 when the grating surface is surrounded by air at normal air pressure.
  • a measure of what a grating can resolve is obtained in the following manner.
  • the width of the image will be mainly determined by the diffraction in the often rectangular aperture that the grating or the focusing optical means defines.
  • W cos ⁇ the width of this aperture.
  • W denotes the width of the grating.
  • the smallest wavelength difference d ⁇ of two wavelengths which are barely resolvable corresponding to this angle change can be obtained from the expression (2).
  • echelle gratings 400 mm wide and the widest echelle gratings that have ever been ruled are 624 mm wide.
  • gratings of such a width require large and expensive optical components for collimating the incident light and for focusing the spectrum on the focal plane.
  • the focal length of these components must be very large (over 10 meters) in order to be able to obtain a sufficiently high linear dispersion so as to be able in practice to make use of the resolution of the grating.
  • the object of the present invention is to provide an apparatus for carrying out spectral analysis by means of which a high resolution can be achieved without using extremely wide gratings and large focal lengths.
  • the invention is based on the following discussion.
  • the angular dispersion from the second grating surface is ##EQU5## where m is the spectral order, d is the grating constant, ⁇ 1 , ⁇ 2 is the angle of incidence and ⁇ 1 , ⁇ 2 the diffraction angles for the respective grating surface.
  • the diffraction grating means comprises at least two grating surfaces so arranged that the radiation, after diffraction from the first grating surface, is subject to diffraction also in the other grating surface or surfaces whereby the grating surfaces have such an orientation that the wavelength dispersion at diffraction from one grating surface acts to increase the wavelength dispersion at diffraction from the following grating surfaces.
  • the same resolution as is obtained with one wide grating is obtained with a plurality of smaller gratings for which the sum of the widths of said gratings equals the width of said grating.
  • the invention also implies that the angular dispersion can be made to be so many times greater than the angular dispersion of one grating as the number of gratings used according to the invention. This implies that the high dispersion which is necessary for the utilization of the high resolution can be produced with focal lengths of the focusing optical components of 1 to 2 m only.
  • the invention implies that both the gratings and the other optical components included are considerably smaller and, accordingly, less expensive than in corresponding instruments provided with one grating.
  • One preferred embodiment of the invention is characterized in that the angle of incidence of the first grating surface is approximately equal to the angle of diffraction of the second grating surface, and that the angle of diffraction of the first grating surface is approximately equal to the angle of incidence of the second grating surface.
  • FIG. 1 shows two grating surfaces arranged according to the invention
  • FIG. 2 shows an arrangement according to the invention with six grating surfaces
  • FIG. 3 illustrates a spectral apparatus utilizing the arrangement according to the invention with 4 grating surfaces.
  • FIG. 1 shows two identical echelle gratings 1 and 2 arranged according to the invention.
  • the incident beams 3 form an angle of incidence ⁇ 1 with the grating surface normal
  • the outgoing beams 5 form an angle of diffraction ⁇ 2 with the normal 4.
  • the angle of incidence ⁇ 1 of the grating 1 is equal to the angle of diffraction ⁇ 2 of the grating 2
  • the angle of diffraction ⁇ 1 of the grating 1 is equal to the angle of incidence ⁇ 2 of the grating 2.
  • the width of the incident beam 3 is denoted by w 1
  • the beam that has been subject to diffraction in the grating 2 has in this case the same width which is denoted by w 2 '.
  • FIG. 2 shows a schematical view of an arrangement according to the invention with six identical echelle gratings 1 to 6.
  • the arrangement comprises three pairs of gratings according to FIG. 1, i.e. the pairs 1 and 2, 3 and 4, as well as 5 and 6.
  • the gratings can preferably be enclosed in an air-tight container in which the gas pressure can be regulated by means for regulating the pressure 60 for scanning different wavelengths and which is provided with means for admitting the radiation into the container and means for recording the spectrum produced 50.
  • a resolution is obtained which is the sum of the resolution of the individual gratings and which corresponds to the resolution of one grating the width of which is the sum of the widths of the individual gratings.
  • 1 and 2 can preferably be arranged so that reflection takes place at the step surfaces of the grooves at diffraction because the highest intensity yield is then obtained from the gratings. This occurs for one wavelength in each spectral order m, denoted ⁇ ' m , for which the angle of incidence ⁇ and the angle of diffraction ⁇ in the equation (1) simultaneously satisfy the condition
  • ⁇ denotes the angle between the normal to the grating surface and the normal to the step surfaces of the grooves. This angle is usually called the blaze angle of the grating.
  • echelle gratings this means that said wavelength range is covered by utilizing diffraction in several spectral orders from the spectral order m min corresponding to ⁇ max to the spectral order m max corresponding to ⁇ min , as appears from equation (1).
  • the pressure is varied in a range from the pressure P 1 to the pressure P 2 , by means for regulating the pressure 60, corresponding to a variation in the refractive index in the surrounding gas from n(P 1 ) to n(P 2 ).
  • the required pressure variation for carrying out the measurement is determined by the requirement that the longest wavelength ⁇ max in the spectral order m min at the pressure P 1 barely can be measured in the next higher spectral order m min +1 at the pressure P 2 .
  • the equation (12) then gives that the required pressure range is determined by the equation ##EQU11## If another wavelength dispersing means is included in the spectral apparatus in order to be able to distinguish the various spectral orders during recording, the entire spectral range from the wavelength ⁇ min to the wavelength ⁇ max can be measured when the pressure is varied from P 1 to P 2 .
  • FIG. 3 A spectral apparatus according to the invention is shown in FIG. 3.
  • 10 denotes the entrance slit.
  • the radiation from this strikes the collimator mirror 11, whereafter the collimated radiation from this mirror in requence strikes the echelle gratings 12, 13, 14 and 15 which are arranged according to the invention.
  • the radiation from the grating 15 is thereafter made to fall on the focusing mirror 16 which focuses the radiation to an image of the entrance slit 16 at the exit slit 17.
  • 18 denotes the walls of a pressure vessel in which windows 19, 20 for the incident and outgoing radiation are fastened.
  • the radiation from the exit slit 17 is passed further into a second pressure vessel 21 provided with similar windows 22 and 23.
  • the pressure vessel 21 communicates with the pressure vessel 18 so that the same pressure prevails in both vessels.
  • the light is passed through the mirror 24 to a wavelength dispersing means 25 which also images the exit slit on the focal plane 26.
  • the radiation from the exit slit 17 will contain only a number of discrete wavelengths, i.e. one wavelength from each spectral order. These wavelengths are determined by the relation ##EQU12## where the constant C has a fixed value, i.e.
  • the number of wavelengths ⁇ ' m is equal to the number of spectral orders, i.e. the difference m max -m min .
  • the different wavelengths ⁇ ' m are imaged on the focal plane 26 at different positions which permit a separate measurement of the intensity of each of these wavelengths.
  • the entire desired spectral range can be measured by recording, at each pressure value, the intensities of these wavelengths in the focal plane 26.
  • all wavelengths at the entrance slit will have been subject to diffraction in the gratings 12 to 15 by utilizing their maximum intensity yield according to equation (12).
  • all wavelengths ⁇ ' m will, because of the pressure vessel 18, during the entire pressure variation be imaged at the same positions in the focal plane 26, which facilitates the recording of their intensities.
  • the focal lengths of the focusing mirror 16 and the collimator mirror 11 are each 1200 mm.
  • the normals 4 of the grating surfaces 1, 2 cross each other. This mutual position of the grating surfaces gives the best results, but also an embodiment where the normals coincide with each other is conceivable.
  • echelle gratings it is possible to use other reflection gratings and also transmission gratings. It is further possible to use gratings having a surface shape other than planar, as well as gratings produced holographically.
  • the invention also includes such mountings of the gratings in which the incident and outgoing radiation of one or more gratings form an angle with the plane which is perpendicular to the grooves in the grating and contains the grating normal.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectrometry And Color Measurement (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
US06/570,930 1982-05-11 1983-05-10 Apparatus for carrying out spectral analysis Expired - Fee Related US4684253A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI821661A FI75047C (sv) 1982-05-11 1982-05-11 Anordning för utförande av spektralanalys.
FI821661 1982-05-11

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US4684253A true US4684253A (en) 1987-08-04

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US (1) US4684253A (de)
EP (1) EP0120870B1 (de)
JP (1) JPS59500984A (de)
DE (1) DE3368462D1 (de)
FI (1) FI75047C (de)
WO (1) WO1983004093A1 (de)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995031703A1 (en) * 1994-05-16 1995-11-23 Now Optics Ab Apparatus for carrying out spectral analysis of an optical light source using image detection and separation of spectral orders
US5675411A (en) * 1996-05-10 1997-10-07 General Atomics Broad-band spectrometer with high resolution
US6151112A (en) * 1997-11-17 2000-11-21 Innovative Lasers Corp. High-resolution, compact intracavity laser spectrometer
WO2002014911A2 (en) * 2000-08-11 2002-02-21 Optichrom Ltd. Double grating for compensating non-linear angular dispersion
WO2003023459A2 (en) * 2001-09-07 2003-03-20 Jobin Yvon Inc. Double grating three dimensional spectrograph
US6538737B2 (en) * 2001-01-29 2003-03-25 Cymer, Inc. High resolution etalon-grating spectrometer
US6667804B1 (en) * 1999-10-12 2003-12-23 Lambda Physik Ag Temperature compensation method for wavemeters

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19635046A1 (de) * 1996-08-29 1998-03-05 Nis Ingenieurgesellschaft Mbh Spektralanalytische Vorrichtung und Verfahren zur Bestimmung von Elementzusammensetzungen und -konzentrationen

Citations (6)

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Publication number Priority date Publication date Assignee Title
US2945953A (en) * 1957-03-19 1960-07-19 Parsons & Co Sir Howard G Grating spectrometers
US3098408A (en) * 1959-02-11 1963-07-23 Applied Physics Corp Double folded-zeta-configuration monochromator
US3373651A (en) * 1966-11-28 1968-03-19 Design Inc Interferometric spectrometer utilizing three fabry-perot etalons in series
US3888590A (en) * 1974-04-10 1975-06-10 John U White Grating monochromator
US3922089A (en) * 1972-03-17 1975-11-25 Nils Allan Danielsson Apparatus and method for the uniform separation of spectral orders
US4455087A (en) * 1981-04-06 1984-06-19 Hamamatsu Systems Inc. Monochromatic imaging apparatus

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US3306158A (en) * 1962-05-29 1967-02-28 Shimadzu Corp Grating spectroscopes
JPS5039693Y1 (de) * 1970-02-25 1975-11-14
FR2125114B1 (de) * 1971-02-11 1973-12-07 Nal Etu Spatia Es Centre
FR2260788A1 (en) * 1974-02-12 1975-09-05 Balkanski Minko Dispersion of a beam of monochromatic radiation - is effected by three monochromators in series improving resolution
JPS5267343A (en) * 1975-10-27 1977-06-03 Hitachi Ltd Double spectroscope
DE2730613C3 (de) * 1977-07-07 1980-04-03 Bodenseewerk Perkin-Elmer & Co Gmbh, 7770 Ueberlingen Doppelmonochromator

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2945953A (en) * 1957-03-19 1960-07-19 Parsons & Co Sir Howard G Grating spectrometers
US3098408A (en) * 1959-02-11 1963-07-23 Applied Physics Corp Double folded-zeta-configuration monochromator
US3373651A (en) * 1966-11-28 1968-03-19 Design Inc Interferometric spectrometer utilizing three fabry-perot etalons in series
US3922089A (en) * 1972-03-17 1975-11-25 Nils Allan Danielsson Apparatus and method for the uniform separation of spectral orders
US3888590A (en) * 1974-04-10 1975-06-10 John U White Grating monochromator
US4455087A (en) * 1981-04-06 1984-06-19 Hamamatsu Systems Inc. Monochromatic imaging apparatus

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
Braund et al., Appl. Optics, V. 19, N. 13, 7/1/80, p. 2146. *
Murty, Appl. Optics, V. 11, N. 10, 10/72, p. 2286. *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995031703A1 (en) * 1994-05-16 1995-11-23 Now Optics Ab Apparatus for carrying out spectral analysis of an optical light source using image detection and separation of spectral orders
US5859702A (en) * 1994-05-16 1999-01-12 Lindblom; Peter Apparatus for carrying out spectral analysis of an optical light source using image detection and separation of spectral orders
US5675411A (en) * 1996-05-10 1997-10-07 General Atomics Broad-band spectrometer with high resolution
US6151112A (en) * 1997-11-17 2000-11-21 Innovative Lasers Corp. High-resolution, compact intracavity laser spectrometer
US6667804B1 (en) * 1999-10-12 2003-12-23 Lambda Physik Ag Temperature compensation method for wavemeters
WO2002014911A2 (en) * 2000-08-11 2002-02-21 Optichrom Ltd. Double grating for compensating non-linear angular dispersion
WO2002014911A3 (en) * 2000-08-11 2003-03-13 Optichrom Ltd Double grating for compensating non-linear angular dispersion
US6538737B2 (en) * 2001-01-29 2003-03-25 Cymer, Inc. High resolution etalon-grating spectrometer
WO2003023459A2 (en) * 2001-09-07 2003-03-20 Jobin Yvon Inc. Double grating three dimensional spectrograph
WO2003023459A3 (en) * 2001-09-07 2003-08-21 Jobin Yvon Inc Double grating three dimensional spectrograph

Also Published As

Publication number Publication date
JPS59500984A (ja) 1984-05-31
FI821661A0 (fi) 1982-05-11
WO1983004093A1 (en) 1983-11-24
FI75047C (sv) 1988-04-11
FI75047B (fi) 1987-12-31
EP0120870B1 (de) 1986-12-17
EP0120870A1 (de) 1984-10-10
DE3368462D1 (en) 1987-01-29

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Owner name: SCANOPTICS OY, VALLIKATU 17, SF-02600 ESPOO 60, FI

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Effective date: 19910804